Analysis of bacterial random motility in a porous medium using magnetic resonance imaging and immunomagnetic labeling.

In this study, we demonstrate the application of immunomagnetic labeling and magnetic resonance imaging (MRI) for the noninvasive visualization of changes in bacterial density distributions as a function of time in a water-saturated porous medium. Magnetite particles (50-60 nm diameter) were attached via a monoclonal antibody to the surface' of Escherichia coli K12 NR50 cells. The cells maintained their motility after labeling, and the presence of the magnetite did not significantly alter cell swimming speed. Diffusive migration for both motile and nonmotile E. coli through a porous medium with a particle-diameter distribution of 250-300 microm was compared. The movement of the nonmotile cells was described by an effective random motility coefficient consistent with Brownian diffusion of a nonmotile colloid. An effective coefficient determined a priori from bacterial motility in an aqueous medium and properties of the porous medium adequately described the movement of the motile cells. The ability to noninvasively visualize bacterial concentrations within an opaque porous medium in real time provides researchers with a powerful tool for studying bacterial transport in porous media. This is important for understanding the impact of bacterial transport on remediation strategies for environmental cleanup of polluted groundwater.